NULL should not be const for RS.

Change-Id: I24d96843c40f822bf064a0fa1fc0440b6bf0518d

Author: stephenhines

libs/rs/scriptc/rs_types.rsh

@@ -364,7 +364,7 @@ typedef struct {
 typedef float4 rs_quaternion;
 
 #define RS_PACKED __attribute__((packed, aligned(4)))
-#define NULL ((const void *)0)
+#define NULL ((void *)0)
 
 #if (defined(RS_VERSION) && (RS_VERSION >= 14))